Maybe some of you have read the article Please don't use Slack for FOSS projects and the related discussion on reddit. Since Slack is about to be established as an important channel for the Kotlin community, I think it is worth to read and think about it.
My favorite solution would be a nice forum with threaded discussions and elements from Stackoverflow.com. But unfortunately there is no such thing … yet.
I think Slack is just another channel. I don't believe it will replace forums and each have their place.
We had/have an IRC channel for Kotlin, but what I can tell you is that it got nowhere near the number of online users or traffic that Slack is currently getting.
One thing I dislike about Slack is that we can't hide our e-mail addresses:
https://twitter.com/SlackHQ/status/531750460940886016
[Edit: Sorry, I had intended to reply to the main post. Still getting used to this forum. 
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Which of the arguments in this post applies to Kotlin, in your opinion? E.g. we coudn't care less whether Slack is open-source or not if it provides a superior experience for our users.